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By an obstetrician-gynecologist with more than 20 years of experience, equipped with modern medical tools to provide comprehensive services for clients.

Rujirek
Obstetrics and Gynecology Clinic

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Down Syndrome Screening

Down Syndrome

Down syndrome is a congenital condition caused by the presence of an extra copy of chromosome 21. It is the most common chromosomal abnormality. Infants with Down syndrome typically have delayed developmental milestones, intellectual disability, and may have associated structural abnormalities involving other organ systems, such as the heart, gastrointestinal tract, and endocrine system.

Who Is at Risk of Having a Child with Down Syndrome?

All pregnant women have a baseline risk of having a baby with Down syndrome. However, the risk increases with maternal age, particularly in women aged 35 years and older, who have a significantly higher likelihood compared to younger mothers.

Screening Methods for Down Syndrome

1. Maternal Age and History of a Previous Child with Down Syndrome

The risk of having a baby with Down syndrome increases with maternal age. In general, women aged over 35 years have a risk higher than 1 in 200 (1:200) for chromosomal abnormalities. However, using maternal age alone as a screening tool has relatively low sensitivity and specificity.

2. Ultrasound Examination

Ultrasound can be used to measure the nuchal translucency (NT)—the fluid-filled space at the back of the fetal neck—between 10 and 14 weeks of gestation. An increased NT measurement is associated with a higher risk of chromosomal abnormalities.
Ultrasound performed at 18–20 weeks may also provide additional indicators that help estimate the level of risk.

3. Maternal Serum Screening

Maternal blood tests measure various biochemical markers produced by the fetus and placenta. These tests help determine whether a pregnant woman is in a high-risk group. Maternal serum screening can be performed in two gestational age windows, and the biochemical markers differ between these periods.

3.1 Maternal Serum Hormone Screening for Down Syndrome

Maternal blood tests can be performed as either first-trimester or second-trimester screening, or both.

1. First-trimester screening (10–14 weeks):
Risk assessment is based on maternal age combined with biochemical markers, including PAPP-A and free β-hCG. This may be performed together with ultrasound measurement of nuchal translucency (NT).

2. Second-trimester screening (15–18 weeks):
Risk assessment combines maternal age with biochemical markers, including AFP, free β-hCG, and uE3—commonly known as the triple screen—and may also include inhibin A (quad screen).

The results are integrated into an overall risk estimate. A calculated risk greater than 1:200–1:300 is considered a positive (abnormal) screening result, and diagnostic chromosomal testing is recommended.

3.2 Non-Invasive Prenatal Testing (NIPT)

NIPT analyzes cell-free fetal DNA circulating in the mother’s blood.
It is the most advanced and highly effective screening method currently available. NIPT can detect trisomy 21 with approximately 99% sensitivity, with a false-positive rate of less than 1%.
However, it is still considered a screening test—not a diagnostic test. If the result is positive and pregnancy termination is being considered, fetal karyotyping is required for confirmation.

NIPT can be performed in almost all pregnant women between 12 and 24 weeks, with the optimal window being 12–16 weeks.

This method is particularly useful in women who are at increased risk of complications from amniocentesis or who have high anxiety regarding invasive procedures—for example, women with multiple previous uterine surgeries or those who conceived through fertility treatments.
However, NIPT is not recommended for women with twin pregnancies or those whose partners carry a chromosomal abnormality such as a balanced translocation.

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